It is known that the pulmonary surfactant is a surface-active substance lining the respiratory system of the lung. Type II pneumocytes produce the surfactant, store it as lamellar bodies and finally express it in the alveolar liquid phase. From there it spreads as a molecular thin film on the air/water boundary surface. It displays its effect by dynamically adapting the surface tension of the boundary surface to the current extension of the boundary surface during the breathing cycle.
Pulmonary surfactant prevents alveolar collapse and flooding at end-expiration, affords patency of small airways and reduces the work required for breathing. Pulmonary surfactant consists of 80-90% (by weight) phospholipids, with a large proportion (−30-45%) being disaturated dipalmitoylphosphatidylcholine (DPPC). The surfactant also contains 50-60% unsaturated phospholipids with reported levels of polyunsaturated species >10% of total phospholipids. Surfactant also contains four surfactant-associated proteins—SP-A, B, C, and D. A highly surface-active form of pulmonary surfactant, referred to as the large aggregate fraction, is enriched in the hydrophobic proteins SP-B and SP-C. Neutral lipids, primarily cholesterol, make up the remaining 2-10% of surfactant.
In 1959 it was shown that the lack of pulmonary surfactant in the lungs of premature infants leads to respiratory distress syndrome (RDS), which at that time was the most frequent cause of death for premature infants. For about the past 15 years, extracts from the lungs of cattle or pigs have been used as a medication to treat RDS. Animal preparations are generally expensive and carry the risk of transmitting infectious diseases.
The surfactant (short for surface active agent) consists of glycero-phospholipids, specific proteins, neutral fats and cholesterol. The surfactant covers the alveolar surface and reduces the surface tension, so that after birth the alveoli do not collapse in the human body during exhalation.
Insufficient function of the surfactant can be the cause of respiratory insufficiency, known as Infant Respiratory Distress Syndrome (IRDS) in premature infants and newborns or in adults as Adult Respiratory Distress Syndrome (ARDS). These lung illnesses are the result of a surfactant deficiency, which lead to an inadequate expansion of the lungs (atelectasis) after a collapse of the pulmonary alveoli.
The lung surfactant consists of 90% lipids and 10% proteins. Although cooperation between the surfactant-specific proteins and the lipids is necessary for a completely functional respiratory process, the lipids are essential for the vitally important reduction of surface tension.
The function of pulmonary surfactants and their inhibited function with pulmonary infections and pulmonary diseases have been described in numerous publications. In this regard reference is made to the publications:
T. R. Martin, Cytokines and the Acute Respiratory Distress Syndrome (ARDS): a question of balance, Nat. Med. 3 (1997), pp. 272.
Artigas, G. R. Bernard, J. Cadet, D. Dreyfuss, L. Gattinoni, The American-European consensus conference on ARDS, part 2: ventilatory, pharmacologic, supportive therapy, study design strategies, and issues related to recovery and remodeling. Acute respiratory distress syndrome, Am. J. Respir. Crit. Care Med. 157 (Pt 1) (1998), pp. 1332.
G. R. Bernard, A. Artigas, K. L. Brigham, J. Carlet, K. Falke, The American-European consensus conference on ARDS: definitions, mechanisms, relevant outcomes, and clinical trial coordination, Am. J. Respir. Crit. Care Med. 149 (1994), pp. 818.
A. B. Montgomery, M. A. Stager, C. J. Carrico, E. D. Hudson, Causes of mortality in patients with the adult respiratory distress syndrome, Am. Rev. Respir. Dis. 132 (1985), pp. 485.
G. Karagiorga, G. Nakos, E. Galiatsou, M. E. Lekka, Biochemical parameters of bronchoalveolar lavage fluid in fat embolism, Intensive Care Medicine 32 (2006), pp. 116-123.
L. D. Hudson, K. P. Steinberg, Epidemiology of acute lung injury and ARDS, Chest 116 (1999), pp. 74S.
G. Devendra, R. G. Spragg, Lung surfactant in subacute pulmonary disease, Respir. Res. 3 (2002), pp. 19.
M. Griese, R. Essl, R. Schmidt, E. Rietschel, F. Ratjen, M. Ballmann, K. Paul, Pulmonary surfactant, lung function, and endobronchial inflammation in cystic fibrosis, American Journal Of Respiratory And Critical Care Medicine 170 (2004), pp. 1000-1005.
M. Griese, L. Felber, K. Reiter, R. Strong, K. Reid, B. H. Belohradsky, G. Jager, T. Nicolai, Airway inflammation in children with tracheostomy, Pediatr. Pulmonol. 37 (2004), pp. 356-361
Bachofen H & Schürch S (2001) Alveolar surface forces and lung architecture. Comparative Biochemistry and Physiology—Part A: Molecular & Integrative Physiology 129: 183-193.
Clements J (1962) Surface phenomena in relation to pulmonary function. Physiologist 5: 11.
Yu S, Harding P G, Smith N & Possmayer F (1983) Bovine pulmonary surfactant: Chemical composition and physical properties. Lipids 18: 522-9.
Veldhuizen R, Nag K, Orgeig S & Possmayer F (1998) The role of lipids in pulmonary surfactant. Biochimica Et Biophysica Acta (BBA)—Molecular Basis of Disease 1408: 90-108.
Yu S, Harding P G R, Smith N & Possmayer F (1983) Bovine pulmonary surfactant: Chemical composition and physical properties. Lipids 18: 522-529.
Postle A D, Heeley E L & Wilton D C (2001) A comparison of the molecular species compositions of mammalian lung surfactant phospholipids. Comparative Biochemistry and Physiology—Part A: Molecular & Integrative Physiology 129: 65-73.
Possmayer F, Nag K, Rodriguez K, Qanbar R & Schurch S (2001) Surface activity in vitro: Role of surfactant proteins. Comp Biochem Physiol A Mol Integr Physiol 129: 209-20.
Pulmonary surfactants form a complex film, which has or plays a critical role in the reduction of surface tension in the respiratory tract in the hydrated air/lung interface. With inflammatory lung diseases, the molecular profile of pulmonary surfactants in the alveoli and respiratory tract is changed so that the pulmonary surfactant film is quite a lot less effective or ineffective for reducing the surface tension, which is accompanied by a strong decrease in the area available for gas exchange.
Furthermore, it is known that an elevated level of cholesterol in the surfactants is a major cause of surfactant dysfunction. In this regard reference is also made to the following publication:
L. Gunasekara, S. Schurch, W. M. Schoel, K. Nag, Z. Leonenko, M. Haufs, M. Amiein, Pulmonary surfactant function is abolished by an elevated proportion of cholesterol, Biochimica Et Biophysica Acta 1737 (2005), 27-35.
Furthermore, it has been shown that the release of reactive oxygen species (ROS) from activated leukocytes or following exposure to environmental pollutants may result in a highly oxidizing milieu within the lungs. Increased levels of reactive oxygen species and their byproducts have been detected from bronchoalveolar lavage fluid collected from patients with ARDS, asthma, CF, ventilator induced lung injury (VILI) or chronic obstructive pulmonary disease (COPD), among many other disease states. Several studies have shown that oxidation of various pulmonary surfactants greatly impairs in vitro and in vivo function, which has so far been largely attributed to oxidative alterations of susceptible residues in SP-B and SP-C, whereas peroxidation and hydrolysis of phospholipids were considered less important. In this regard reference is also made to the following publications:
K. Rodriguez-Capote, D. Manzanares, T. Haines, F. Possmayer, Reactive oxygen species inactivation of surfactant involves structural and functional alterations to surfactant proteins SP-B and SP-C, Biophysical Journal 90 (2006), 2808.
S. Andersson, A. Kheiter, T. A. Merritt, Oxidative inactivation of surfactants, Lung 177 (1999), 179.
L. Mark, E. P. Ingenito, Surfactant function and composition after free radical exposure generated by transition metals, Am. J. Physiol.—lung Cell. Mol. Physiol. 276 (1999), L491.
N. Gilliard, G. P. Heldt, J. Loredo, H. Gasser, H. Redl, T. A. Merritt, R. G. Spragg, Exposure of the hydrophobic components of porcine lung surfactant to oxidant stress alters surface tension properties, Journal Of Clinical Investigation 93 (1994), 2608.
Lang J D, McArdle P J, O'Reilly P J & Matalon S (2002) Oxidant-antioxidant balance in acute lung injury*. Chest 122: 314S-320S.
Ciencewicki J, Trivedi S & Kleeberger S R (2008) Oxidants and the pathogenesis of lung diseases. J Allergy Clin Immunol 122: 456-468.
Lamb N J, Gutteridge J, Baker C, Evans T W & Quinlan G J (1999) Oxidative damage to proteins of bronchoalveolar lavage fluid in patients with acute respiratory distress syndrome: Evidence for neutrophil-mediated hydroxylation, nitration, and chlorination. Crit. Care Med 27: 1738.
Andersson S, Kheiter A & Merritt T (1999) Oxidative inactivation of surfactants. Lung 177: 179-189.
Bailey T C, et al (2006) Physiological effects of oxidized exogenous surfactant in vivo: Effects of high tidal volume and surfactant protein A. American Journal of Physiology—Lung Cellular and Molecular Physiology 291: L703-L709.
Gilliard N, et al (1994) Exposure of the hydrophobic components of porcine lung surfactant to oxidant stress alters surface tension properties. J Clin Invest 93: 2608.
Haddad I Y, et al (1993) Mechanisms of peroxynitrite-induced injury to pulmonary surfactants. American Journal of Physiology—Lung Cellular and Molecular Physiology 265: L555-L564.
Mark L & Ingenito E (1999) Surfactant function and composition after free radical exposure generated by transition metals. American Journal of Physiology—Lung Cellular and Molecular Physiology 276: L491-L500.
Stenger P C, et al (2009) Environmental tobacco smoke effects on lung surfactant film organization. Biochimica Et Biophysica Acta (BBA)—Biomembranes 1788: 358-370.
Rodriguez-Capote K, Manzanares D, Haines T & Possmayer F (2006) Reactive oxygen species inactivation of surfactant involves structural and functional alterations to surfactant proteins SP-B and SP-C. Biophys J 90: 2808-2821.
Manzanares D, et al (2007) Modification of tryptophan and methionine residues is implicated in the oxidative inactivation of surfactant protein B. Biochemistry 46: 5604-5615.
Keating E, et al (2007) Effect of cholesterol on the biophysical and physiological properties of a clinical pulmonary surfactant. Biophys J 93: 1391-1401.
This invention addresses the unaddressed question concerning the contribution of cholesterol to oxidation-induced surfactant dysfunction. In particular, it remained unknown, until this invention; whether oxidative alterations to surfactant interact with normal or increased levels of cholesterol to negatively affect surfactant function.